The requirement for HNF4 in hepatic development has been previously documented through the generation of mice lacking HNF4. The series of experiments outlined in this proposal aim to determine which transcriptional targets of HNF4 contribute to regulation of differentiation and epithelial formation of the liver. Initial experiments have identified 20 genes with known roles in epithelial formation arid cell adhesion functions downregulated in the liver upon HNF4 loss. The importance of these targets in regulating hepatic differentiation will be tested by viral-mediated knockdown of expression in a culture system that mimics many hepatic features. To determine whether these targets are sufficient to rescue the phenotype of HNF4 null livers, expression of the targets will be reconstituted in progenitor cells from the livers of HNF4 loxP/loxP mice treated with adenoviral-Cre. Finally, the in vivo developmental function of the target or targets with the most profound affect on hepatic differentiation will be studied through the generation of knockout and/or liver-conditional knockout mice. These studies will provide understanding of the HNF4-mediated signaling cascade mediating development of the liver, and the molecular and cellular processes these signals control. [unreadable] [unreadable]